Process of producing all skin rayon



United States Patent PROCESS OF PRODUCHVG ALL SKIN RAYON Harry H. Hall, Drexel Hill, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Application December 30, 1954 Serial No. 478,913

6 Claims. (Cl. 18-54) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton 'linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it. is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is. subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either be fore or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these dilferent portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stilf.

It has now been discovered that the presence of small amounts of alkali-soluble phosphoric acid esters of alkylene oxide adducts of higher aliphatic alcohols in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of all skinand having improved properties and characteristics providing that the amount of the ester is maintained with certain limits and the composition of 2,895,787. Patented July 21, 1959 ICC tion limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

The higher aliphatic alcohols are straight chain mono-' hydric alcohols containing from 6 to 24 carbon atoms; and may be saturated or unsaturated. The alcohol may be obtained from the fatty acids derived from animal and vegetable fats and oils, such as coconut oil, cotton seed oil, corn oil, soya bean oil, palm oils, peanut oil; tallow and the like and the hydrogenated fats and oils. The term higher aliphatic alcohol ,is used herein to designate these straight chain monohydric, primary alcohols and includes such alcohols whether prepared fnonl fats and oils or from other sources. The higher aliphatic, alcohol employed in preparing the substances as utilized for the purposes of this invention may be a pure compound, such as lauryl or oleyl alcohol or the higher aliphatic alcohol may consist of a mixture of alcohols where the aliphatic alcohols are obtained from a mixture of fatty acids of a particular fat or oil such as coconut oil.

The adducts, or as more technically classed, the poly! oxyalkylene glycol mono-ethers, may be prepared by reacting a higher aliphatic alcohol, or a mixture, of higher aliphatic alcohols with an alkylene oxide or a polyoxyale kylene glycol whereby one of the hydroxyl groups of the glycol is etherified. Adducts or ethers which are satisfactory for the purposes of this invention may be derived from capryl, lauryl, myristyl, oleyl, stearyl and like alcohols or from a mixture of higher aliphatic alcohols such as derived from the fatty acids of coconut oil or other fat or oil.

The alkylene oxide adducts or polyoxyalkylene glycol ethers of the higher aliphatic alcohols may have at least about 2 to about 20 or more alkylene oxide units per molecule, preferably between about 4 and 10- alkylene oxide units per molecule of the higher aliphatic alcohol. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and in alkali solutions, the ethylene oxide adducts or polyoxyethylene glycol ethers are preferred. For purposes of illustration only, the invention is described by reference to the ethylene oxide adducts but it is to be understood that other alkylene oxide ad.- ducts such as propylene oxide adducts are equally satisfactory.

the spinning bath is maintained within certain composi- The modifiers employed in the present invention may be any of the phosphoric acid esters, namely, the monc-, di-, or tri-esters, with the polyoxyalkylene glycol mono.- ethers of the higher aliphatic alcohols. In accordance with conventional practice the term phosphoric acid is used to designate the ortho form or modification of the acid. The mono-, diand tri-esters designate compounds in which 1, 2, and 3 hydroxyl groups of the acid have been esterified with the polyoxyalkylene glycol monoethers of the higher aliphatic alcohol. In the monoand di-esters, the remaining active hydrogen atoms of the acid may be replaced with an alkali metal such as sodium, potassium and the like. Thus the invention contemplates the use of mono-, di-, and tri-esters. of phosphoric acid with the alkylene oxide adduct of the higher aliphatic a1. cohol and monoand di-esters of the diand mono-alkali metal salts of phosphoric acid with alkylene oxide adducts of the higher aliphatic alcohols, respectively.

The various esters of the ethers or alkylene oxide. ad ducts are satisfactory providing they possess the required solubility. That is, the ester must have sufficient solu: bility to permit a minimum amount of the ester to be dissolved in the viscose.

The amount of the ester or modifier which is incorporated in the viscose must be at least about 0.25% by weight of the cellulose in the viscose and may vary up to about 4%, preferably, the amount varies from 0.5 to 2.5%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within thepreferred range are most effective in enhancing the characteristics and properties of the products. The ester may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of ,viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or afterrfiltration. The ester is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

"The viscose may contain from about 6% to about 8% cellulose, the particularsource of the cellulose being selected for the ultimate used of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose co taining the small amount of a phosphoric acid ester may have a salt test above about 7 and preferably above about 8 at the time of spinning or extrusion. The term salt test as used herein refers to the conventional sodium chloride salt test.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of the ester in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high abrasion re- 'sistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zincspinning bath containing from about 10% to about 25% sodium sulfate and from about 3% to about zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 C., preferably between about 45 C. and about 70 C. In the production of the all skin type filaments, the temperature of the spinning bath is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spin- 'ning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength. The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated' viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the sp'nning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufliciently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufficiently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the. all skin products from a 7% cellulose, 6%

caustic-viscose and containing the phosphoric acid esters lies between about 5% and about 8%. The acid concentration may be increased as the amount of the ester is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of ester and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of the ester is increased beyond about 4% while other conditions are maintained constant. Increasing the caustic soda content of the viscose beyond about 8% is uneconomical for commercial production methods. For example, a viscose containing about 7% cellulose, about 6% caustic soda, about 41% (based on the weight of cellulose) carbon disulfide, and 1% (based on the weight of cellulose) of a di-ester of phosphoric acid with a polyoxyethylene glycol. mono-ether of lauryl alcohol, the ether containing 4 ethylene oxide units per molecule, and having a salt test of about 8 when extruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid not more than about 8% results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed. Greater amounts of sulfuric acid result in the production of products having skin and core. A lowering of the amount of the ester, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. It has been determined that the maximum concentration of acid which is permissible for the production of all skin products is about-8.5%.

The presence of the ester in the viscose retards the coagulation and, therefore, the amount of ester employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the ester is employed in amounts within the lower portion of the range, for example, about 0.6% to 0.75%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufiicient to effect relatively complete coagulation of the viscose, that is, the coagulation must be suflicient so that the filaments will not-adhere to each other as they are brought together and withdrawn from the bath.

.In. general, a closer control of the spinning conditions must be maintained in order to produce all skin products of relatively large cross-section such as filaments above about 6 to 8 denier. It-has been discovered that by the use of the esters as described herein, all skin products of relatively large cross-section such as filaments above about 6 to 8 denier may be readily produced without maintaining the close control and that as the cross-section is decreased, a closer control of the spinning conditions must be maintained. I

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to about 120%, preferably between and Yarns for other textile purposes maybe stretched as low as 20%. The precise amount of stretching will'be dependent upon the desired tenacity and other properties and the specific type of product being produced. If desired, the filaments may be stretched in air. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, filn1s, tubes and; the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

I The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof. 7

Regenerated cellulose filaments prepared from viscose containing the small amounts of the phosphoric acid esters and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared -from viscose containing the phosphoric acid esters have superior abrasion and fatigue resistance characteristics and have a high flex-life as compared to normal regenerated cellulose filaments. Such filaments are high ly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, carpet and rug fibers or yarns and the like, but the filaments are not restricted to such uses and may be used for other textile applications. I

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7% cellulose, about 6.5% caustic soda, and having a total carbon disulfide content of about 35% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2/2 hours. The cellulose xanthate was then dissolved in caustic soda solution. An additional 5% carbon disulfide was then added to the mixer and the mass mixed for about one hour. The desired amount of a phosphoric acid ester of an polyoxyethylene glycol mono-ether of a fatty alcohol was added to the solution and mixed about Me hour. The viscose was then allowed to ripen for about 30 hours at 18 C.

Example 1 Approximately 1% (based on the weight of the cellulose) of a phosphoric acid ester was added to and incorporated in the viscose as described above. The additive or modifier was a tri-ester of phosphoric acid and a polyoxyethylene glycol mono-ether of oleyl alcohol containing about 4 ethylene oxide units per molecule of oleyl alcohol. The viscose employed in the spinning of filaments had a salt test of 8.5 and was extruded through a spinneret to form a 340 denier, 40 filament yarn at a rate of about 25 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 7.3% sulfuric acid, 8.7% zinc sulfate and 19% sodium sulfate. The yarn was passed over a godet from which it was conducted to threadadvancing reels where it was stretched about 57%, washed free of acids and salts with hot water (98 C.), dried and collected on cones.

The individual filaments have a smooth, non-crenulated Example 2 To a viscose as described above, there was added 1% (based on the weight of the cellulose) of a monosodium di-ester of phosphoric acid and a polyoxyethylene glycol mono-ether of oleyl alcohol containing about 8 ethylene oxide units per molecule of oleyl alcohol. The viscose had a salt test of 7.8 and was spun into a 344 denier, 40 filament yarn by extrusion into a spinning bath containing 7.4% sulfuric acid, 8.7% zinc sulfate and 19% sodium sulfate. The bath was maintained at 60 C. and the extrusion rate was about 25 meters per minute. The filaments were subsequently passed over a godet from which they were conducted to thread-advancing reels and stretched about 57%, washed free of acids and salts with hot water (98 0), dried and collected on cones.

The individual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin while the control filaments have a very irregular and serrated surface and consist of about 65 skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 3 To a viscose solution as described above, there was added 1% (based on the weight of the cellulose) of a tri-ester of phosphoric acid and a polyoxyethylene glycol mono-ether of lauryl alcohol containing 4 ethylene oxide units per molecule of lauryl alcohol. The viscose 'had a salt test of 9.0 and was spun into a 316 denier, 40 filament yarn by extrusion into a bath containing 7.8% sulfuric acid, 8.6% zinc sulfate and 19% sodium sulfate. The bath was maintained at a temperature of 60 C. The extrusion rate was about 25 meters per minute. The yarn was passed over a godet from which it was conducted to thread-advancing reels where it was stretched about 57%, washed free of acid and salts with hot water (98 C.), dried and collected on cones.

The individual filaments were readily distinguishable fronicontrol filaments prepared from viscose containing no ester in that they have a smooth, non-crenlulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of about 65 skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 4 To a viscose solution as described above, there was added about 1% (based on the weight of the cellulose) of a mono-sodium di-ester of phosphoric acid and a polyoxyethylene glycol mono-ether of lauryl alcohol containing about 4 ethylene oxide units per molecule of lauryl alcohol. The viscose had a salt test of 8.1 and was spun into a 336 denier, 40 filament yarn by extrusion into a bath containing 7.5% sulfuric acid, 8.1% zinc sulfate and 19% sodium sulfate. The bath was maintained at a temperature of about 60 C. The extrusion rate was about 25 meters per minute. The yarn was passed over a godet from which it was conducted to thread-advancing reels where it was stretched about 57%, washed free of acid and salts with hot Water (98 C.), dried and collected on cones.

The individual filaments were readily distinguishable from control filaments in that, they have a smooth, noncre'nulatedsurface and consist entirely of skin whereas control filaments have a very irregular and serrated surface and consist of about 65% skin and the balance core with a sharp line of demarkation between the skin and the core. Other characteristics are set forth in the table which follows:

Tenacity, Elongation, grams per percent denier Skin,

- percent Wet Dry Wet Dry Example 1.-- 1. 1 2. 26 21 100 Example 2.-. 1. 6 2. 3 32 22 100 Example 3-- 1. 0 1. 8 27 18 100 Example 4. 1. 7 2. 4 29 20 100 Control a 65 1 Not determined.

.wet withwater, this swelling amounting to from about 65 to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The phosphoric acid esters may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The adducts may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinning.

If desired, small amounts of the ester may be added to the spinning bath. Since the substances are also watersoluble, some of the ester will be leached from the filaments and will be present in the bath.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyer's albumin fixative. After dewaxing in xylene, the section is placed in sucessive :baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for l to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and 90% dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have .been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

' 1. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing from about 0.25% to about 4%, based on the weight of the cellulose, of a modifier selected from the group consisting of alkali-soluble esters of phosphoric acid and alkali- .solubleiesters of alkali-metal acid salts of phosphoric acid with polyoxyalkylene glycol mono-ethers of higher aliphatic alcohols into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8.5%, the polyoxyalkylene glycolmono-ether of the higher aliphatic alcohol containing at least about 2 alkylene oxide units per molecule of higher aliphatic alcohol.

2. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the steps which comprise adding to and inoorporating'in viscose from about 0.25 to about 4.0%, based on the weight of the cellulose, of a modifier selected from the group consisting of alkali-soluble esters of phosphoric acid and alkali-soluble esters of alkali-metal acid salts of phosphoric acid with polyoxyalkylene glycol monoethers of higher aliphatic alcohols, the ether of the higher aliphatic alcohol containing at least about 2 alkylene oxide units per molecule of higher aliphatic alcohol, and extruding the viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8.5%.

3. The steps in the method as defined in claim 2 wherein the modifier is an ester of phosphoric acid.

4. The steps in the method as defined in claim 2 wherein the modifier is an ester of an alkali-metal salt of phosphoric acid.

5. The steps in the method as defined in claim 2 wherein the modifier is an ester of a polyoxyethylene glycol mono-ether of a higher aliphatic alcohol.

6. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from 0.5% to 2.5%, based on the weight of the cellulose, of a modifier selected from the group consisting of alkali-soluble esters of phosphoric acid and alkalimetal esters of alkali-metal acid salts of phosphoric acid with polyoxyethylene glycol mono-ethers of higher aliphatic alcohols, the ethers of the higher aliphatic alcohols containing from about 2 to 10 ethylene oxide units per molecule of higher aliphatic alcohol, ripening the viscose to a salt point of not less than 8 and extruding the viscose into an aqueous spinning bath containing from about 16% to 20% sodium sulfate, from about 4% to 9% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8.5%.

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1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEP WHICH COMPRISES EXTRUDING VISCOSE CONTAINING FROM ABOUT 0.25% TO ABOUT 4% BASED ON THE WEIGHT OF THE CELLULOSE, OF A MODIFER SELECTED FROM THE GROUP CONSISTING OF ALKALI-SOLUBLE ESTERS OF PHOSPHORIC ACID ADN ALKALI SOLUBLE ESTERS OF ALKALI-METAL ACID SALTS OF PHOSPHORIC ACID WITH POLYOXYALKYLENE GLYCOL MONO-ETHERS OF HIGHER ALIPHATIC ALCOHOLS INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO 25% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINC SULFATE AND SULFURIC ACID, THE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 8.5% THE POLYOXYALKYLENE GLYCOL MONO-ETHER OF THE HIGHER ALIPHATIC ALCOHOL CONTAINING AT LEAST ABOUT 2 ALKYLENE OXIDE UNITS PER MOLECULE OF HIGHER ALIPHATIC ALCOHOL. 